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  • #46
    Thank you.

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    • #47
      Originally posted by A.K. Boomer View Post
      Well, CarlB is *almost* right on that one; https://www.caranddriver.com/feature...plugs-feature/
      Two rules when quoting car articles:
      1) Never trust a five year old article.
      2) Never trust an article written by Don Sherman.

      The article is from 2014 and apparently Hyundai has backed off on the idea of GDCI. See :https://www.autoblog.com/2018/09/24/...engines-grant/. Check back in 10 years.

      In other news, Mazda's Skyactiv-X, which blends spark and compression ignition, is available in Europe now and in North America 'Real Soon Now' which means 'someday, maybe'. Here ya go: https://www.motor1.com/news/346378/m...-engine-delay/

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      • #48
        Fair enough Carlb, but iv read about countless other variations over the years - some using a type of glow-plug just for starting but once the engine heat builds up it does not need any extra help, that's allot like certain diesels, it's just a matter of time, your concerns about injector life are warranted but Digs have been in full production for quite sometime now and I have not heard of anything out of the ordinary...

        but the main thing I was stating is they really are getting immune to the old school thought of "mixture"

        it's copious amounts of air and just add whatever fuel you need to it be it little or lot, they are wide open throttle all the time, they pump through many times more air then an old school gasser, to think that they are still stoichiometric would mean piss poor economy - but that's not the case because they are immune to having to match the air with the fuel ratio, they operate more like a diesel, that's what you get when you put the injector INSIDE the combustion chamber...

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        • #49
          Originally posted by A.K. Boomer View Post
          ..... they pump through many times more air then an old school gasser, .....
          Seems like it's the same old swept volume x number of admission strokes, with an effective manifold pressure adjustment... just like always. "many times more air" would imply more displacement, or much higher rpm......

          Possibly you mean "more air than the gas used would imply".... Stratified charge does that.

          BTW, the gasoline engine has the potential for much higher efficiency than diesel. That comes straight from Carnot. But the EPA will not allow it, due to NOx production at the temps necessary to realize it.
          1601 2137 5683 1002 1437

          Keep eye on ball.
          Hashim Khan

          If you look closely at a digital signal, you find out it is really analog......

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          • #50
            Originally posted by J Tiers View Post
            Seems like it's the same old swept volume x number of admission strokes, with an effective manifold pressure adjustment... just like always. "many times more air" would imply more displacement, or much higher rpm......
            JT - they don't have throttle plates - there wide open to "air" this is just like a diesel, at idle they take in many times more air possibly 10 or 100 times, they are FULL BORE WIDE OPEN and no that's not "just like always" and it does not imply "more displacement" or "higher RPM"

            Possibly you mean "more air than the gas used would imply".... Stratified charge does that.
            no - it blows stratified charge out of the ballpark, your talking 14+ to 1 compression ratio's WITH using a turbocharger,,, that's the miracle of micro managing the injection rate's and pulses...
            BTW, the gasoline engine has the potential for much higher efficiency than diesel. That comes straight from Carnot. But the EPA will not allow it, due to NOx production at the temps necessary to realize it.
            I did not know this - I always thought if we get to abandoned the emissions thing then the winner of efficiency goes to the diesel simply for carrying more BTU's per gallon... interested in what your saying so please explain...

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            • #51
              Originally posted by A.K. Boomer View Post
              JT - they don't have throttle plates - there wide open to "air" this is just like a diesel, at idle they take in many times more air possibly 10 or 100 times, they are FULL BORE WIDE OPEN and no that's not "just like always" and it does not imply "more displacement" or "higher RPM" no - it blows stratified charge out of the ballpark, your talking 14+ to 1 compression ratio's WITH using a turbocharger,,, that's the miracle of micro managing the injection rate's and pulses...


              I did not know this - I always thought if we get to abandoned the emissions thing then the winner of efficiency goes to the diesel simply for carrying more BTU's per gallon... interested in what your saying so please explain...
              The engine may be at "full bore", but it still can take in no more air than the cylinder volume x the number of intake strokes, as modified by manifold pressure (higher if turbo,and including flow related pressure drops)....... and, it has to be stratified charge, because despite the crowing about "forget stoichiometric ratio", it still has to LOCALLY have the correct ratio, or it will not go "boom" (there are limits of flammability). That's nearly the definition of stratified charge, and I believe you said so yourself.......

              As for no throttle plate, that has nothing whatever to do with it. Puts only enough fuel in to equal the power needed.... if it put in more, the engine would accelerate until the load DID equal the fuel burn power (at efficiency). Works as well as a throttle. Better, actually. Air flow is constant at a given rpm, but fuel burn is related to power needed at that rpm.

              Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

              The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.
              Last edited by J Tiers; 06-16-2019, 01:57 AM.
              1601 2137 5683 1002 1437

              Keep eye on ball.
              Hashim Khan

              If you look closely at a digital signal, you find out it is really analog......

              Comment


              • #52
                Originally posted by CarlByrns View Post
                Boomer GDI engines that work as a normal spark-ignition engine and slide into a compression-ignition regime under certain conditions. Preignition is avoided by the simple fact there is no fuel in the cylinder. I'd imagine the injection pressure is astronomical and without diesel's lubricity, injector wear is bound to be an issue.
                Yes Sir Carl. JR

                +
                My old yahoo group. Bridgeport Mill Group

                https://groups.yahoo.com/neo/groups/...port_mill/info

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                • #53
                  Originally posted by J Tiers View Post

                  Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

                  The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.
                  Theoretical cycle for spark ignited engines is modeled as a constant volume combustion. Or in other words the combustion occurs instantaneously at TDC. Theoretical cycle for compression ignition is modeled as constant pressure combustion. Or in other words the combustion occurs on the expansion stroke. More realistic model for both is a blend of the two models. Constant volume model results in greater Carnot efficiency. Just another way to describe what Tiers is saying.

                  https://www.google.com/url?sa=i&sour...60773934123074

                  This subject has been of great interest to me since I was a kid. And I do have graduate level education to back it up. Enjoy the discussion!

                  Comment


                  • #54
                    Diesel fuel molecular structure has long straight carbon chains. This encourages autoignition quickly so the fuel starts to burn as soon as it is injected.

                    Gasoline is the opposite. Highly branched molecular structure to DISCOURAGE autoignition so the fuel does not start to burn until spark ignited.

                    Using diesel in a gas engine results in early autoignition and knocking. Using gasoline in a diesel engine results in lots of fuel injected before autoignition resulting again in knock. Very different combustion processes.

                    I don't understand why we don't just build diesels. This blending of the two does not make sense to me.

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                    • #55
                      My understanding is that modern gasoline is composed primarily of straight chain (alkane) compnents of length up to 10 or 12 or so.

                      Ed
                      For just a little more, you can do it yourself!

                      Comment


                      • #56
                        [QUOTE]
                        Originally posted by strokersix;1243212..................
                        ............................

                        I don't understand why we don't just build diesels. This blending of the two does not make sense to me.[/QUOTE
                        It boils down to dollars and cents and the economic viability of using diesel as a fuel despite some of it's inherent advantages.
                        Emissions compliance has added at least 10-15,000 dollars to the cost of large truck engines. Add to this system maintenance and increased operational costs due to the complexity of these very integrated systems.

                        Particulate matter emissions reductions have exceeded 98% and NOX has been reduced at least 95% from pre-emission enhancement technology days but clean air comes at a cost. Gasoline being somewhat easier to clean up, either in-cylinder or by using after-treatment is becoming more of a viable option in areas where diesel used to be the first choice.
                        Home, down in the valley behind the Red Angus
                        Bad Decisions Make Good Stories​

                        Location: British Columbia

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                        • #57
                          Originally posted by J Tiers View Post
                          The engine may be at "full bore", but it still can take in no more air than the cylinder volume x the number of intake strokes, as modified by manifold pressure (higher if turbo,and including flow related pressure drops)....... and, it has to be stratified charge, because despite the crowing about "forget stoichiometric ratio", it still has to LOCALLY have the correct ratio, or it will not go "boom" (there are limits of flammability). That's nearly the definition of stratified charge, and I believe you said so yourself.......
                          Your right technically it is the definition of a highly advanced stratified charged engine - but not to be confused with yesteryears, but we were comparing the old gassers to the new Dig's, and i used idle or mild load as an example,
                          the old gassers do not even come close to filling up their chamber due to a throttle plate that is all but totally cutting off their air supply, the Dig's are taking in 10 fold if not 100 fold amount of air in comparison,,, this has NOTHING to do with engine displacement or turbo charging,,, one is restricted - the other is not, And yes you can "forget about stoichiometric ratio" as some kind of solid guideline throughout the engines range, unless you plan on including more flexible ratios of 60+:1

                          , it's why I used idle and mild load as an initial example, even the old school stratified charge engines could only make mild gains in comparison... again were talking turbo charged engines with 14:1 compression ratio's --- that's incredible... and they are now the dominant force in production vehicles... it's what everyone is going to...



                          As for no throttle plate, that has nothing whatever to do with it. Puts only enough fuel in to equal the power needed.... if it put in more, the engine would accelerate until the load DID equal the fuel burn power (at efficiency). Works as well as a throttle. Better, actually. Air flow is constant at a given rpm, but fuel burn is related to power needed at that rpm.
                          maybe this will help , the old gassers were at the mercy of controlling their flame front and burn rate by using mixture ratios's , the Dig's get to function more like diesels and are "somewhat" IMMUNE to this fact, they control their flame front and burn rate with injection...

                          Carnot efficiency is related to the difference in temperature between starting state, and final state of the "working fluid" in the energy extraction process (power stroke, here), so long as it is used efficiently, and assuming no loss to cylinder walls etc. That's the very very short story, and no doubt one of the usual suspects will quibble and squall, but that won't make it false. It's why there was a flap about ceramic engines to work at high temps, back in the 1960s. then they discovered that NOx was a pollutant, and that anything over about 2300 deg or thereabouts made it in quantity.

                          The peak temp in a gas engine as traditionally made, is quite high, higher than the usual diesel, so the Carnot efficiency can be higher. It generally is not, and there are plenty of details, but it could be.

                          yes im familiar with Smokey Yunicks ceramic engines and such, iv just never heard anyone use that as the holy grail for judging that Gas is more efficient then Diesel, there's no reason you can't also create a diesel to run to extreme temps, i mean if you get to toss emissions out the window then so do I, I would think tie goes to the fuel with the greater BTU rating --? heat it up and burn it and see what you get...
                          Last edited by A.K. Boomer; 06-16-2019, 11:29 AM.

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                          • #58
                            This discussion does make me wonder about combustion chamber "hot spots" that were so dreaded for the old gassers as they could cause the fuel to go off under compression,,, so would not the answer for the new Dig's be creating one? as in an initial glow plug to help the engine start and then it sits there out in front of the injector nozzle glowing red hot waiting for it's next "spritz" of fuel,,,
                            perhaps there is still an advantage to being able to control spark and injector timing and that's why it has not been done,


                            these newer little engines are amazing - the honda CRV for example needed a NA 2.4 liter to push it around and now it's got a 1.5 turbo that's not only faster but has about 1/3rd better fuel economy... Before Dig's you would shoot yourself in the foot expecting to do better in economy by throwing a turbo charger on an engine, in fact why honda never used them...

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                            • #59
                              Originally posted by A.K. Boomer View Post
                              .....

                              yes im familiar with Smokey Yunicks ceramic engines and such, iv just never heard anyone use that as the holy grail for judging that Gas is more efficient then Diesel, there's no reason you can't also create a diesel to run to extreme temps, i mean if you get to toss emissions out the window then so do I, I would think tie goes to the fuel with the greater BTU rating --? heat it up and burn it and see what you get...
                              Never heard of SY's ceramic engines...... talking about research engines at universities etc. SY was a tinkerer... a smart tinkerer but not a researcher. probably the whole thing is moot, since the diesel is gradually having its present advantage legislated away, and gas engine technology is improving.

                              if you are talking miles per gallon, or some such, you are off-base, like measuring liquid volume by wind speed........

                              It is nearly meaningless, and a function ONLY of the stupid american habit of measuring chemicals by volume. At the very least, you would want to measure by mass, and in reality, you would want to measure fuel by net energy content of the amount sold, because THAT is what you are buying.

                              The true efficiency is the amount of energy extracted, compared to the energy content of the fuel to begin with.
                              1601 2137 5683 1002 1437

                              Keep eye on ball.
                              Hashim Khan

                              If you look closely at a digital signal, you find out it is really analog......

                              Comment


                              • #60
                                Originally posted by J Tiers View Post

                                The true efficiency is the amount of energy extracted, compared to the energy content of the fuel to begin with.
                                Now that level's the playing field - then it all comes down to engine operating principle and design...

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